1. Field of the Invention
The invention relates to belt tensioning devices, and in particular to spring-biased belt tensioning devices for use with the endless drive belts of the drive systems for vehicle accessories. More particularly, the invention relates to an extremely simple and inexpensive belt tensioner operable by a compression coil spring which applies a nearly constant predetermined tensioning force on the endless drive belt by an idler pulley or by pivotal movement of one of the vehicle accessories, and in which a one-way clutch prevents movement of the idler pulley or accessory in the opposite nontensioning direction.
2. Description of the Prior Art
There is the trend today in the automobile industry to operate the various vehicle accessories, such as the power steering pump, oil and air pumps, air conditioning and alternator, by a single endless belt driven by a pulley connected to the engine crankshaft. This system is referred to as a "serpentine" drive belt system. To ensure optimum operating efficiency for these various accessories, it is necessary that the drive belt be maintained at a predetermined tension to assure efficient performance of the accessories as well as satisfactory service life for the belt. Due to the relatively greater length for the single drive belt which replaces the heretofore plurality of smaller belts, there is a greater tendency for the belt to stretch which will affect the operating characteristics of the driven accessories. Therefore, it is desirable that a belt tensioning device be used for these endless belts to provide reliable service over an extended period of time and to maintain a constant amount of tension thereon regardless of the amount of belt stretch.
Numerous devices have been proposed and used to accomplish this purpose. One type of tensioner uses a bushing formed of an elastomeric material which is placed in compression by some mechanical means for continuously exerting a tensioning force on the belt. Examples of these constructions are shown in U.S. Pat. Nos. 3,975,965 and 4,144,772. These tensioner constructions, which use an elastomeric material, have the disadvantages in that the high load rate which they exert on the belt results in the rapid loss of tensioning as the belt stretches, and this load rate limits the stroke of the belt-engaged idler pulley to a shorter distance than desired. Also, sudden acceleration and deceleration of the drive belt can cause a whipping action to occur which creates a time lag before full damping is achieved.
Numerous other types of belt tensioning devices use coil springs which are either in compression or tension, for applying and maintaining the tensioning force on a belt-engaging idler pulley or chain-engaging sprocket. Some examples of these types of constructions are shown in U.S. Pat. Nos. 2,703,019, 2,893,255, 3,413,866, 3,483,763, 3,631,734, 3,768,324, 3,812,733, 3,924,483, 3,965,768 and 4,108,013. Some of these various coil spring-actuated devices use the biasing force of a spring in combination with hydraulic-actuated members for regulating the amount of tensioning force applied to the belt, depending on whether the engine is running or shut off. Examples of these combination spring and hydraulic belt tensioners are shown in U.S. Pat. Nos. 2,051,488, 3,142,193 and 4,077,272.
Other known types of belt tensioners and tensioning arrangements will pivot one of the vehicle accessories toward belt tensioning engagement either by springs, as shown in U.S. Pat. Nos. 3,768,324 and 3,924,483, or by a hydraulic snubber, as shown in U.S. Pat. No. 3,132,596.
Other types of tensioning devices and arrangements are provided with some type of mechanical retaining means, usually a ratchet-pawl retaining mechanism, which limits the movement of the belt tensioning member in an opposite nontensioning direction, thereby maintaining a constant tensioning force on the endless drive belt and eliminating the undesirable effects of belt whipping. Examples of these prior constructions and arrangements having such retaining mechanisms are shown in U.S. Pat. Nos. 2,051,488, 2,703,019, 3,413,866, 3,631,734 and 3,812,733.
There is no known belt tensioning device of which I am aware which imparts a nearly constant predetermined tensioning force on an endless accessory drive belt by use of a compression coil spring in a simple and inexpensive arrangement, which maintains this nearly constant pressure on the belt whether the engine is on or off or operating at various speeds, and which reduces belt whip and achieves a highly efficient damping effect by a one-way clutch which prevents retraction of the tensioning components from their forwardmost belt tensioning position.